Peracid compositions have been reported to be effective antimicrobial agents. Methods to clean, disinfect, and/or sanitize hard surfaces, meat products, living plant tissues, and medical devices against undesirable microbial growth have been described (U.S. Pat. No. 6,545,047; U.S. Pat. No. 6,183,807; U.S. Pat. No. 6,518,307; U.S. patent application publication 20030026846; and U.S. Pat. No. 5,683,724). Peracids have also been reported to be useful in preparing bleaching compositions for laundry detergent applications (U.S. Pat. No. 3,974,082; U.S. Pat. No. 5,296,161; and U.S. Pat. No. 5,364,554).
Peracids can be prepared by the chemical reaction of a carboxylic acid and hydrogen peroxide (see Organic Peroxides, Daniel Swern, ed., Vol. 1, pp 313-516; Wiley Interscience, New York, 1971). The reaction is usually catalyzed by a strong inorganic acid, such as concentrated sulfuric acid. The reaction of hydrogen peroxide with a carboxylic acid is an equilibrium reaction, and the production of peracid is favored by the use of an excess concentration of peroxide and/or carboxylic acid, or by the removal of water.
Enzyme catalysts can also catalyze the rapid production of peracid at the time of use and/or application, avoiding the need for storage of peracid solutions, which may cause peracid concentration to decrease over time. The high concentrations of carboxylic acids typically used to produce peracid via the direct chemical reaction with hydrogen peroxide are not required for enzymatic production of peracid, where the enzyme-catalyzed reaction can use a carboxylic acid ester as substrate at a much lower concentration than is typically used in the chemical reaction. The enzyme-catalyzed reaction can be performed across a broad range of pH, depending on enzyme activity and stability at a given pH, and on the substrate specificity for perhydrolysis at a given pH.
Esterases, lipases and some proteases have the ability to catalyze the hydrolysis of alkyl esters to produce the corresponding carboxylic acids (Formula 1):
                                                        R              1                        ⁢                                          COO                ⁢                R                            2                                +                                    H              2                        ⁢            O                          ⁢                  ->                                    Lipase              ,              esterase              ,              or                        protease                          ⁢                                            R              1                        ⁢            COOH                    +                                                    HO                ⁢                R                            2                        .                                              Formula        ⁢                                  ⁢        1            
Some esterases, lipases, and proteases also exhibit perhydrolysis activity, catalyzing the synthesis of peracids from alkyl esters (Formula 2):
                                                        R              1                        ⁢                                          COO                ⁢                R                            2                                +                                    H              2                        ⁢                          O              2                                      ⁢                  ->                                    Lipase              ,              esterase              ,              or                        protease                          ⁢                                            R              1                        ⁢            COOOH                    +                                                    HO                ⁢                R                            2                        .                                              Formula        ⁢                                  ⁢        2            
The CE-7 class of carbohydrate esterases has been found to have highly specific activity for perhydrolysis of esters, particularly acetyl esters of alcohols, diols and glycerols. U.S. patent application Ser. Nos. 11/638,635; 11/743,354; 11/943,872; and 12/143,375 to DiCosimo et al disclose enzymes structurally classified as members of the CE-7 family of carbohydrate esterases (e.g., cephalosporin C deacetylases [CAHs] and acetyl xylan esterases [AXEs]) that are characterized by significant perhydrolysis activity for converting carboxylic acid esters (in the presence of a suitable source of peroxygen, such as hydrogen peroxide) into peroxycarboxylic acids at concentrations sufficient for use as a disinfectant and/or a bleaching agent. Under certain reaction conditions, CE-7 esterases can catalyze the production of concentrations of peracid at least as high as 4000-5000 ppm in 1 min and up to at least 9000 ppm in 5 min to 30 min (U.S. patent application Ser. No. 12/143,375 to DiCosimo et al). Peroxycarboxylic acids can be corrosive to certain metal surfaces, however, so it may be desirable to limit the total amount of peracid produced during the reaction to prevent or minimize the corrosive effect of the resulting solution. For example, applications that require production of no more than 200 ppm to 1000 ppm of peracid in 1 minute often employ reaction conditions that yield a final concentration of peracid well above these limits. In an application for in situ generation of peracid for disinfection of hard surfaces, it is desirable to have the ability to rapidly generate the desired concentration of peracid without significantly exceeding the upper efficacious disinfectant concentration, thereby limiting or preventing the corrosion of certain components of the surface. In an application for in situ generation of peracid for bleaching of laundry or textiles, similar limitations to the concentration of peracid generated above that required for bleaching are also desirable.
In addition to catalyzing the production of peracids, CE-7 esterases can also catalyze the hydrolysis of peracid to produce carboxylic acid and hydrogen peroxide. Therefore, under reaction conditions where the enzyme retains its activity for an extended period of time, it may destroy the peracid produced in the first enzyme-catalyzed reaction of ester and peroxide, producing carboxylic acid (e.g., acetic acid) as a byproduct that can impart an undesirable odor to the disinfectant solution. This peracid hydrolysis activity of the enzyme could also jeopardize the long term stability of peracid-containing formulations produced by CE-7 esterases over the course of several hours, or even several days or weeks, depending on the stability of the peracid in the disinfectant formulation.
Peracid solutions have a wide variety of applications. Though progress has been made in devising efficient and effective ways to produce peracid solutions, improved methods are needed. An in situ process for producing peracids that limits the enzyme-catalyzed production of peracids in a peracid concentration-dependent manner would allow targeted concentrations of peracids to be produced in a task-appropriate way.